Multi-layer release films

ABSTRACT

A multilayer film includes a first layer including a blend of a polyolefin and a diene elastomer and a second layer directly contacting and directly bonded to the first layer. The second layer includes a fluoropolymer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of and claims priorityfrom U.S. Utility patent application Ser. No. 10/663,288, filed Sep. 16,2003, entitled “MULTILAYER STRUCTURE WITH INTERCROSSLINKED POLYMERLAYERS,” naming inventors Alexander Tukachinsky, Michael L. Friedman,and Paul W. Ortiz, which is a continuation-in-part of and claimspriority from U.S. Utility patent application Ser. No. 09/873,612, nowU.S. Pat. No. 6,652,943, filed Jun. 4, 2001, which applications areincorporated by reference herein in their entirety.

FIELD OF THE DISCLOSURE

This disclosure, in general, relates to multi-layer release films andmethods for making such films.

BACKGROUND

Increasingly, manufacturers are seeking polymers to create surfaces thatare resistant to chemical and environmental damage. In addition,manufacturers are seeking films that have release characteristics,forming a surface that is resistant to adhesion with other surfaces. Inparticular applications, films formed of such polymers have been used asairplane and train cargo holders, vinyl siding surface treatments,photovoltaic protective coverings, and release films. An example of suchpolymers includes low surface energy polymers. Low surface energypolymers, such as fluoropolymers, exhibit a resistant to damage causedby exposure to chemicals, such as methyl ethyl ketone (MEK), have aresistance to stains, demonstrate a resistance to damage caused byexposure to environmental conditions, and typically, form a releasesurface.

While such low surface energy polymers are in demand, the polymers tendto be expensive. In addition, such polymers exhibit low wettingcharacteristics and given their tendency to form a release surface,adhere poorly with other polymer substrates. For particularfluoropolymers, such as PVDF, manufacturers have turned to adhesivelayers including acrylic polymers to adhere the fluoropolymer layer toincompatible substrates. However, acrylic polymers are typically lesstolerant of environmental stresses, such as ultraviolet light exposureand high temperature. As such, the bond between a fluoropolymer layerfilm and an underlying substrate may degrade with time. Moreover,mismatches between mechanical properties of an underlying substrate anda fluoropolymer layer degrade the contact between the layers and thesubstrate with ongoing mechanical stress, resulting in reduced peelstrength and a potential degradation of the bond between thefluoropolymer layer and the underlying film layers.

As such, an improved multi-layer film and a method for manufacturingsuch multi-layer films would be desirable.

SUMMARY

In a particular embodiment, a multilayer film includes a first layerincluding a blend of a polyolefin and a diene elastomer and a secondlayer directly contacting and directly bonded to the first layer. Thesecond layer includes a fluoropolymer.

In another exemplary embodiment, a multilayer film includes a firstlayer including a blend of polyolefin and ethylene propylene dienemonomer (EPDM) elastomer and includes a second layer directly contactingand directly bonded to the first layer. The second layer includes afluoropolymer.

In a further exemplary embodiment, a multilayer film includes a firstlayer comprising a blend of polyolefin and ethylene propylene dienemonomer (EPDM) elastomer. The polyolefin is selected from the groupconsisting of polyethylene and polypropylene. The multilayer film alsoincludes a second layer directly contacting and directly bonded to thefirst layer. The second layer includes fluorinated ethylene propylenecopolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes an illustration of an exemplary multi-layer film.

FIG. 2 includes a graphical illustration of data representing thethermal performance of blends of polyolefin and diene elastomer.

DESCRIPTION OF THE DRAWINGS

In a particular embodiment, a multi-layer film includes first and secondlayers. The first layer may include a blend of a diene elastomer and apolyolefin. For example, the blend may include a diene elastomer and atleast about 40% by weight polyolefin. The second layer includes a lowsurface energy polymer. For example, the low surface energy polymer mayinclude a fluoropolymer. The second layer is bonded directly to anddirectly contacts the first layer. In an exemplary embodiment, themulti-layer film may also include a third layer bonded directly to anddirectly contacting the first layer. The third layer may include, forexample, the low surface energy polymer. In a particular example, thesecond and third layers form opposite outermost layers of themulti-layer film.

In an exemplary embodiment, the multi-layer film may be formed byblending a diene elastomer and at least 40% by weight of a polyolefin. Amulti-layer film including first and second layers may be extruded. Thefirst layer includes the blend of diene elastomer and polyolefin. Thesecond layer includes a low surface energy polymer. In an exemplaryembodiment, the first and second layers are coextruded so as to directlycontact each other. In addition, the first layer may be cured, such asthrough crosslinking. For example, the multi-layer film may be exposedto radiation, such as e-beam radiation or ultraviolet electromagneticradiation. Alternatively, water activated crosslinking agents may beused to cure the polymer blend of the first layer.

As illustrated in FIG. 1, a multi-layer film 100 may include a layer102, which forms an outermost surface 112. The layer 102 may be bondedto a layer 104 along a major surface 108 of the layer 104. In anexemplary embodiment, the multi-layer film 100 includes two layers, suchas the layer 102 and the layer 104. Alternatively, the multi-layer film100 may include two or more layers, such as three layers. For example, athird layer 106 may be bonded to a second major surface 110 of the layer104. The second major surface 110 is, for example, a major surfaceopposite the major surface 108. In such an example, the third layer 106may form an outermost surface 114 opposite the outermost surface 112. Ina further alternative embodiment, the layer 104 may be formed ofmultiple core or intermediate layers.

In general, the intermediate layer 104 has greater thickness than theoutermost layer 102 or optional outermost layer 106. For example, anoutermost layer, such as the layer 102 and optionally, the layer 106,may form not greater than about 20% by volume of the multi-layer film100. For example, the layer 102 may form not greater than about 15% byvolume of the multi-layer film 100, such as not greater than about 10%by volume of the multi-layer film 100. The intermediate layer 104 mayform at least about 60% by volume of the multi-layer film 100, such asat least about 70% by volume or at least about 80% by volume of themulti-layer film 100. The total film thickness of the multi-layer film100 may be at least about 13 microns. For example, the multi-layer film100 may have a total thickness of at least about 25 microns, such as atleast about 50 microns, at least about 100 microns, or as high as 200microns or higher.

In an exemplary embodiment, the layer 102 includes a low surface energypolymer. For example, a low surface energy polymer may be a polymer thathas a tendency to form a low surface energy surface. In an example, alow surface energy polymer includes a fluoropolymer. An exemplaryfluoropolymer may be formed of a homopolymer, copolymer, terpolymer, orpolymer blend formed from a monomer, such as tetrafluoroethylene,hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene,vinylidene fluoride, vinyl fluoride, perfluoropropyl vinyl ether,perfluoromethyl vinyl ether, or any combination thereof. An exemplaryfluoropolymer includes a fluorinated ethylene propylene copolymer (FEP),a copolymer of tetrafluoroethylene and perpfluoropropyl vinyl ether(PFA), a copolymer of tetrafluoroethylene and perfluoromethyl vinylether (MFA), a copolymer of ethylene and tetrafluoroethylene (ETFE), acopolymer of ethylene and chlorotrifluoroethylene (ECTFE),polychlorotrifluoroethylene (PCTFE), poly vinylidene fluoride (PVDF), aterpolymer including tetrafluoroethylene, hexafluoropropylene, andvinylidenefluoride (THV), or any blend or any alloy thereof. Forexample, the fluoropolymer may include FEP. In a further example, thefluoropolymer may include PVDF. In an exemplary embodiment, thefluoropolymer may be a polymer crosslinkable through radiation, such ase-beam. An exemplary crosslinkable fluoropolymer may include ETFE, THV,PVDF, or any combination thereof. A THV resin is available from Dyneon3M Corporation Minneapolis, Minn. An ECTFE polymer is available fromAusimont Corporation (Italy) under the trade name Halar. Otherfluoropolymers used herein may be obtained from Daikin (Japan) andDuPont (USA). In particular, FEP fluoropolymers are commerciallyavailable from Daikin, such as NP-12X.

In an exemplary embodiment, the layer 104 includes an elastomericmaterial. In a particular embodiment, the elastomeric material includesa crosslinkable elastomeric polymer. For example, the layer 104 mayinclude a diene elastomer. In a particular example, the elastomericmaterial includes a blend of a diene elastomer and a polyolefin. In aparticular example, the diene elastomer is a copolymer formed from atleast one diene monomer. For example, the diene elastomer may be acopolymer of ethylene, propylene and diene monomer (EPDM). An exemplarydiene monomer includes a conjugated diene, such as butadiene, isoprene,chloroprene, or the like; a non-conjugated diene including from 5 toabout 25 carbon atoms, such as 1,4-pentadiene, 1,4-hexadiene,1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene, 1,4-octadiene, or the like; acyclic diene, such as cyclopentadiene, cyclohexadiene, cyclooctadiene,dicyclopentadiene, or the like; a vinyl cyclic ene, such as1-vinyl-1-cyclopentene, 1-vinyl-1-cyclohexene, or the like; analkylbicyclononadiene, such as 3-methylbicyclo-(4,2,1)-nona-3,7-diene,or the like; an indene, such as methyl tetrahydroindene, or the like; analkenyl norbornene, such as 5-ethylidene-2-norbornene,5-butylidene-2-norbornene, 2-methallyl-5-norbornene,2-isopropenyl-5-norbornene, 5-(1,5-hexadienyl)-2-norbornene,5-(3,7-octadienyl)-2-norbornene, or the like; a tricyclodiene, such as3-methyltricyclo (5,2,1,0²,6)-deca-3,8-diene or the like; or anycombination thereof. In a particular embodiment, the diene includes anon-conjugated diene. In another embodiment, the diene elastomerincludes alkenyl norborene. The diene elastomer may include, forexample, ethylene from about 63 wt % to about 95 wt % of the polymer,propylene from about 5 wt % to about 37 wt %, and the diene monomer fromabout 0.2 wt % to about 15 wt %, based upon the total weight of thediene elastomer. In a particular example, the ethylene content is fromabout 70 wt % to about 90 wt %, propylene from about 17 wt % to about 31wt %, and the diene monomer from about 2 wt % to about 10 wt % of thediene elastomer. The diene elastomer typically has a Mooney viscosity ofat least about 20, such as about 25 to about 150 (ML 1+8 at 125° C.). Inan exemplary embodiment, the diene elastomer has a dilute solutionviscosity (DSV) of at least about 1, such as about 1.3 to about 3measured at 25° C. as a solution of 0.1 grams of diene polymer perdeciliter of toluene. Prior to crosslinking, the diene elastomer mayhave a green tensile strength of about 800 psi to about 1,800 psi, suchas about 900 psi to about 1,600 psi. The uncrosslinked diene elastomermay have an elongation at break of at least about 600 percent. Ingeneral, the diene elastomer includes a small amount of a diene monomer,such as a dicyclopentadiene, a ethylnorborene, a methylnorborene, anon-conjugated hexadiene, or the like, and typically have a numberaverage molecular weight of from about 50,000 to about 100,000.Exemplary diene elastomers are commercially available under thetradename Nordel from Dow Dupont.

The polyolefin of the blend may include a homopolymer, a copolymer, aterpolymer, an alloy, or any combination thereof formed from a monomer,such as ethylene, propylene, butene, pentene, methyl pentene, octene, orany combination thereof. An exemplary polyolefin includes high densitypolyethylene (HDPE), medium density polyethylene (MDPE), low densitypolyethylene (LDPE), ultra low density polyethylene, ethylene propylenecopolymer, ethylene butene copolymer, polypropylene (PP), polybutene,polypentene, polymethylpentene, polystyrene, ethylene propylene rubber(EPR), ethylene octene copolymer, or any combination thereof. In aparticular example, the polyolefin includes high density polyethylene.In another example, the polyolefin includes polypropylene. In a furtherexample, the polyolefin includes ethylene octene copolymer. In aparticular embodiment, the polyolefin is not a modified polyolefin, suchas a carboxylic functional group modified polyolefin, and in particular,is not ethylene vinyl acetate. In addition, the polyolefin is not formedfrom a diene monomer. In a particular example, the polyolefin has adegree of crystallinity. For example, the polyolefin may have at leastabout 35% crystallinity. In a particular example, the polyolefin mayhave a crystallinity of at least about 50%, such as at least about 60%or at least about 70% crystallinity. In a particular example, thepolyolefin may be a high crystallinity polyolefin. Alternatively, thepolyolefin may be a low crystallinity polyolefin, having a crystallinitynot greater than 35%. Low crystallinity polyolefins may enhanceconformability of release films or improve clarity. An exemplarycommercially available polyolefin includes Equistar 8540, an ethyleneoctene copolymer; Equistar GA-502-024, an LLDPE; Dow DMDA-8904NT 7, anHDPE; Basell Pro-Fax SR275M, a random polypropylene copolymer; Dow 7C50,a block PP copolymer; or products formerly sold under the tradenameEngage by Dupont Dow.

In an example, the blend includes not greater than about 40 wt %polyolefin, such as not greater than about 30 wt % polyolefin. Forexample, the blends may include not greater than about 20 wt % of thepolyolefin, such as not greater than 10 wt %. In a particular example,the blend includes about 5 wt % to about 30 wt %, such as about 10 wt %to about 30 wt %, about 10 wt % to about 25 wt %, or about 10 wt % toabout 20 wt %.

In general, the blend exhibits compatibility between the polymericcomponents. DMA analysis may provide evidence of compatibility. DMAanalysis may show a single tan delta peak between glass transitiontemperatures of major components of a blend, indicating compatibility.Alternatively, an incompatible blend may exhibit more than one tan deltapeak. In an example, the blend may exhibit a single tan delta peak. Inparticular, the single tan delta peak may be between the glasstransition temperature of the polyolefin and the glass transitiontemperature of the diene elastomer.

In general, blend may be cured through cross-linking. In a particularexample, the diene elastomer may be cross-linkable through radiation,such as using X-ray radiation, gamma radiation, ultravioletelectromagnetic radiation, visible light radiation, electron beam(e-beam) radiation, or any combination thereof. Ultraviolet (UV)radiation may include radiation at a wavelength or a plurality ofwavelengths in the range of from 170 nm to 400 nm, such as in the rangeof 170 nm to 220 nm. Ionizing radiation includes high-energy radiationcapable of generating ions and includes electron beam (e-beam)radiation, gamma radiation, and x-ray radiation. In a particularexample, e-beam ionizing radiation includes an electron beam generatedby a Van de Graaff generator, an electron-accelerator, or an x-ray. Inan alternative embodiment, the diene elastomer may be crosslinkablethrough thermal methods. In a further example, the diene elastomer maybe crosslinkable through chemical reaction, such as a reaction between asilane crosslinking agent and water.

In an exemplary embodiment, the blend may further include a crosslinkingagent, a photoinitiator, a filler, a plasticizer, or any combinationthereof. Alternatively, the blend may be free of crosslinking agents,photoinitiators, fillers, or plasticizers. In particular, the blend maybe free of photoinitiators or crosslinking agents.

To facilitate crosslinking, the material of the elastomeric layer 104may include a photoinitiator or a sensibilizer composition. For example,when ultra-violet radiation is contemplated as the form of irradiationor when e-beam radiation is contemplated as the form of irradiation, thematerial may include a photoinitiator to increase the crosslinkingefficiency, i.e., degree of crosslinking per unit dose of radiation.

An exemplary photoinitiator includes benzophenone, ortho- andpara-methoxybenzophenone, dimethylbenzophenone, dimethoxybenzophenone,diphenoxybenzophenone, acetophenone, o-methoxy-acetophenone,acenaphthene-quinone, methyl ethyl ketone, valerophenone, hexanophenone,alpha-phenyl-butyrophenone, p-morpholinopropiophenone, dibenzosuberone,4-morpholinobenzo-phenone, benzoin, benzoin methyl ether,3-o-morpholinodeoxybenzoin, p-diacetyl-benzene, 4-aminobenzophenone,4′-methoxyacetophenone, alpha-tetralone, 9-acetylphenanthrene,2-acetyl-phenanthrene, 10-thioxanthenone, 3-acetyl-phenanthrene,3-acetylindole, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene,thioxanthen-9-one, xanthene-9-one, 7-H-benz[de]anthracen-7-one, benzointetrahydrophyranyl ether, 4,4′-bis(dimethylamino)-benzophenone,1′-acetonaphthone, 2′ acetonaphthone, aceto-naphthone and2,3-butanedione, benz[a]anthracene-7,12-dione,2,2-dimethoxy-2-phenylaceto-phenone, alpha-diethoxy-acetophenone,alpha-dibutoxy-acetophenone, anthraquinone, isopropylthioxanthone, orany combination thereof. An exemplary polymeric initiator may includepoly(ethylene/carbon monoxide),oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)-phenyl]propanone],polymethylvinyl ketone, polyvinylaryl ketones, or any combinationthereof.

Another exemplary photoinitiator includes benzophenone; anthrone;xanthone; the Irgacure® series of photoinitiators from Ciba-Geigy Corp.including 2,2-dimethoxy-2-phenylacetophenone (Irgacure® 651),1-hydroxycyclohexylphenyl ketone (Irgacure® 184), or2-methyl-1-[4-(methylthio)phenyl]-2-moropholino propan-1-one (Irgacure®907); or any combination thereof. Generally, the photoinitiator exhibitslow migration from the material of the elastomeric layer 104. Inaddition, the photoinitiator typically has a low vapor pressure atextrusion temperatures and sufficient solubility in the polymer orpolymer blends of the elastomeric layer 104 to yield efficientcrosslinking. In an exemplary embodiment, the vapor pressure andsolubility, or polymer compatibility, of the photoinitiator may beimproved by derivatizing the photoinitiator. An exemplary derivatizedphotoinitiator includes, for example, higher molecular weightderivatives of benzophenone, such as 4-phenylbenzophenone,4-allyloxybenzophenone, 4-dodecyloxybenzophenone, or any combinationthereof. In an example, the photoinitiator may be covalently bonded to apolymer of the material of the elastomeric layer 104.

In an exemplary embodiment, the material of the elastomeric layer 104includes about 0.0 wt % to about 3.0 wt % photoinitiator, such as about0.1 wt % to about 2.0 wt %.

Crosslinking may also be facilitated by a chemical crosslinking agent,such as a peroxide, an amine, a silane, or any combination thereof. Inan exemplary embodiment, the material of the elastomeric layer 104 maybe prepared by dry blending solid state forms of polymer and thecrosslinking agent, i.e., in powder form. Alternatively, the materialmay be prepared in liquid form, sorbed in inert powdered support or bypreparing coated pellets, or the like.

An exemplary thermally activatable crosslinking agent includes a freeradical generating chemical, which when exposed to heat decomposes toform at least one, and typically two or more free radicals to effectcrosslinking. In an exemplary embodiment, the crosslinking agent is anorganic crosslinking agent including an organic peroxide, an amine, asilane, or any combination thereof.

An exemplary organic peroxide includes2,7-dimethyl-2,7-di(t-butylperoxy)octadiyne-3,5;2,7-dimethyl-2,7-di(peroxy ethyl carbonate)octadiyne-3,5;3,6-dimethyl-3,6-di(peroxy ethyl carbonate)octyne-4;3,6-dimethyl-3,6-(t-butylperoxy)octyne-4;2,5-dimethyl-2,5-di(peroxybenzoate)hexyne-3;2,5-dimethyl-2,5-di(peroxy-n-propyl carbonate)hexyne-3;2,5-dimethyl-2,5-di(peroxy isobutyl carbonate)hexyne-3;2,5-dimethyl-2,5-di(peroxy ethyl carbonate)hexyne-3;2,5-dimethyl-2,5-di(alpha-cumyl peroxy)hexyne-3;2,5-dimethyl-2,5-di(peroxy beta-chloroethyl carbonate) hexyne-3;2,5-dimethyl-2,5-di(t-butylperoxy) hexyne-3; or any combination thereof.A particular crosslinking agent is 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, available from Elf Atochem under the trade designationLupersol 130. Another exemplary crosslinking agent is dicumyl peroxide,available from Elf Atochem as Luperox 500R. In a particular embodiment,the crosslinking agent is present in the material in an amount betweenabout 0.1 wt % to about 5.0 wt %, such as about 0.5 wt % to about 2.0 wt% based on the weight of the material.

An exemplary silane crosslinking agent has the general formula:

in which R1 is a hydrogen atom or methyl group; x and y are 0 or 1 withthe proviso that when x is 1, y is 1; n is an integer from 1 to 12,preferably 1 to 4, and each R independently is a hydrolyzable organicgroup such as an alkoxy group having from 1 to 12 carbon atoms (e.g.,methoxy, ethoxy, butoxy), aryloxy group (e.g., phenoxy), araloxy group(e.g., benzyloxy), aliphatic acyloxy group having from 1 to 12 carbonatoms (e.g., formyloxy, acetyloxy, propanoyloxy), amino or substitutedamino groups (e.g., alkylamino, arylamino), or a lower alkyl grouphaving 1 to 6 carbon atoms, with the proviso that not more than one ofthe three R groups is an alkyl. Such silanes may be grafted to a polymerthrough the use of an organic peroxide. Additional ingredients such asheat and light stabilizers, pigments, or any combination thereof, alsomay be included in the material. In general, the crosslinking reactionmay result from a reaction between the grafted silane groups and water.Water may permeate into the bulk polymer from the atmosphere or from awater bath or “sauna”. An exemplary silane includes an unsaturatedsilane that comprise an ethylenically unsaturated hydrocarbyl group,such as a vinyl, allyl, isopropenyl, butenyl, cyclohexenyl orgamma-(meth)acryloxy allyl group, and a hydrolyzable group, such as, forexample, a hydrocarbyloxy, hydrocarbonyloxy, or hydrocarbylamino group.An example of a hydrolyzable group includes a methoxy group, an ethoxygroup, a formyloxy group, an acetoxy group, a proprionyloxy group, analkyl group, an arylamino group, or any combination thereof. Aparticular silane is an unsaturated alkoxy silanes that can be graftedonto the polymer. In particular, the silane may include vinyl trimethoxysilane, vinyl triethoxy silane, gamma-(meth)acryloxy propyl trimethoxysilane, or any combination thereof.

The amount of silane crosslinker may vary widely depending upon thenature of the blend, the silane, the processing conditions, the graftingefficiency, the ultimate application, and similar factors. Typically, atleast 0.5 parts per hundred resin (phr), such as at least about 0.7 phr,is used. Generally, the amount of silane crosslinker does not exceed 5phr, such as not greater than about 2 phr.

In another exemplary embodiment, an amine crosslinking agent may includea monoalkyl, duallyl or trialkyl monoamine, wherein the alkyl groupcontains from about 2 to about 14 carbon atoms; a trialkylene diamine ofthe formula N(R²)₃N; a dialkylene diamine of the formula HN(R²)₂NH; analkylene diamine, H₂NR²NH₂; a dialkylene triamine, H₂NR²NHR²NH₂; analiphatic amine having a cyclic chain of from four to six carbon atoms;or any combination thereof. The alkylene group R² in the above formulaemay include from about 2 to about 14 carbon atoms. An exemplary cyclicamine may have a heteroatom, such as oxygen, for example, an N-alkylmorpholine. Another exemplary cyclic amine includes pyridine,N,N-dialkyl cyclohexylamine, or any combination thereof. An exemplaryamine is triethylamine; di-n-propylamine; tri-n-propylamine;n-butylamine; cyclohexylamine; triethylenediamine; ethylenediamine;propylenediamine; hexamethylenediamine; N,N-diethyl cyclohexylamine;pyridine; ethyl-p-dimethyl amine benzoate (EDAB); octyl-p-dimethylaminobenzoate (ODAB); or any combination thereof. In an exemplaryembodiment, the material includes from about 0.5 wt % to about 10.0 wt %of the amine.

In a particular example, curing is enhanced using FirstCure ITX,available from Albemarle, Inc. FirstCure ITX may also be used inconjunction with an amine synergist, such as ethyl-p-dimethyl aminebenzoate (EDAB) or octyl-p-dimethyl aminobenzoate (ODAB).

Returning to FIG. 1, the multi-layer film 100 may be formed through amethod, such as coextrusion, colamination, extrusion lamination, meltcoating of a preformed layer, or comolding. In particular, co-extrusionmay produce a film or a sheet. For example, a sheet of each layer 102,104, and optionally, 106 may be extruded and placed together while in aheat-softened condition in the co-extrusion die or after the outlet ofthe die to form a pre-formed article. When chemical crosslinkers arepresent, crosslinking may occur. Alternatively, the sheet may besubjected to radiation crosslinking.

Once the multilayer article is pre-formed, crosslinking may beperformed. In an example, crosslinking may effect bonding of the layers102, 104, and optionally, 106 together. Such crosslinking may altermechanical properties of the elastomeric layer 104 and improve peelstrength between the layers 102, 104, and 106. Crosslinking may beperformed at elevated temperature, such as when the layers 102, 104, andoptionally, 106 are placed together at above the melting point of eithercomponent, at room temperature, or at any temperature in between.

To illustrate crosslinking by radiation, a film is prepared by theextrusion process. In the extrusion process, the material of layer 102,the material of layer 104, and optionally, the material of layer 106 maybe separately melted and separately supplied or jointly melted andsupplied to a co-extrusion feed block and die head wherein a filmincluding the layers 102, 104, and optionally 106 is generated. Anexemplary die employs a “coat hanger” type configuration. An exemplarylinear coat hanger die head is commercially available from ExtrusionDies, Inc. (Connecticut) or Cloeren Die Corp., (Texas). In an exemplaryembodiment, the coextruded multilayer film is drawn at a ratio notgreater than 30:1, such as not greater than 20:1. Alternatively, theextruded layers may be pressed together at pressures in the range of 0.1MPa to 80 MPa.

Once the film is formed, radiation crosslinking may be immediatelyperformed and the film may be rolled. Alternatively, the film may berolled in an uncrosslinked state, unrolled at a later time and subjectedto radiation crosslinking.

The radiation may be effective to create crosslinks in the crosslinkablepolymer of the layer 104. The intralayer crosslinking of polymermolecules within the layer 104 provides a cured composition and impartsstructural strength to the layer 104 of the multi-layer film 100. Inaddition, radiation may effect a bond between an outermost layer 102formed of a fluoropolymer and the core layer 104, such as throughinterlayer crosslinking. In a particular embodiment, the combination ofinterlayer crosslinking bonds between the layers and the cured corelayer present an integrated composite that is highly resistant todelamination, has a high quality of adhesion resistant and protectivesurface, incorporates a minimum amount of adhesion resistant material,and yet, is physically substantial for convenient handling anddeployment of the multilayer film 100. For example, the multilayer filmmay exhibit a peel strength of at least about 5 gm/cm of width, whentested in standard “T”-Peel configuration at room temperature. Inparticular, thinner films below 1 mil in thickness may have a peelstrength of at least about 5 gm/cm, such as at least about 10 gm/cm. Inanother example, the peel strength of the multilayer film may be atleast about 30 gm/cm, such as at least about 40 gm/cm, at least about 45gm/cm, or even at least about 50 gm/cm. In particular, thicker films orfilms used in conjunction with adhesive tapes over a wide temperaturerange may have peel strengths of at least about 30 gm/cm.

In a particular embodiment, the radiation may be ultravioletelectromagnetic radiation having a wavelength between 170 nm and 400 nm,such as about 170 nm to about 220 nm. Crosslinking may be effected usingat least about 120 J/cm² radiation.

Once formed and cured, the multi-layer polymer film may exhibitdesirable mechanical properties. For example, the multi-layer polymerfilm may have a tensile strength of at least about 12 MPa, based on ASTMD882-02 testing methods. For example, the multi-layer film may have atensile strength of at least about 15 MPa, such as at least about 20MPa.

In another exemplary embodiment, the multi-layer film exhibits adesirable elongation at ultimate tensile strength based on ASTM D882-02testing methods. For example, the multi-layer film may exhibit anelongation at ultimate tensile strength of at least about 145%, such asat least about 170% or at least about 200%.

Particular embodiments of a multilayer film including a core layerformed of a blend of EPDM and polyolefin and including an outermostlayer formed of fluoropolymer may advantageously exhibit improvedmechanical properties while maintaining crosslinkability and interlayerbonding. For example, embodiments of a multilayer film including a corelayer formed of a blend of EPDM and not greater than about 40 wt %polyolefin and an outermost layer of fluoropolymer may exhibit improvedtensile strength and elongation at ultimate tensile strength. Furtherembodiments of a multilayer film including a core layer formed of ablend of EPDM and not greater than about 40 wt % polyolefin and anoutermost layer of fluoropolymer may exhibit intracrosslinking withinthe core layer and bonding between the core layer and the outermostlayer of fluoropolymer without the use of an intervening adhesive layer.In addition, embodiments including a blend may include layers thatexhibit similar responses to mechanical stress, reducing interfacialseparating in response to mechanical stress.

EXAMPLES

Five polymers are selected for a blending study. Specifically, blendsare formed that include EPDM and one of five commercially availablepolyolefins. The commercially available polyolefins are Equistar 8540,an ethylene octene copolymer; Equistar GA-502-024, an LLDPE; DowDMDA-8904NT 7, an HDPE; Basell Pro-Fax SR275M, a random polypropylenecopolymer; and Dow 7C50, a block PP copolymer. The selected EPDM gradeis Nordel 4725, available from Dupont-Dow. A blend including the EPDMand at least one polyolefin is included as an intermediate or core layerof a multi-layer film that includes outermost layers formed from DaikinNP-12X FEP. The multi-layer film is coextruded and exposed toultraviolet electromagnetic radiation, curing the blend of the corelayer.

The multi-layer films are coextruded to 1 mil in thickness and exposedto ultraviolet radiation generated by an H+ bulb included in a Fusion UVSystems Model VPS-6 system. The samples are exposed through multiplepasses to ultraviolet radiation for a total exposure of 129 J/cm². Theblends did not include a photoinitiator.

Example 1

Dynamic mechanical analysis (DMA) is used to evaluate the compatibilityof the blends. The tan delta peak of a DMA scan provides the glasstransition temperature (T_(g)) for the overall blend. In a compatiblesystem, the T_(g) moves according to the relative amounts of eachcomponent in the binary blend, i.e., the T_(g) for the blend has anintermediate value relative to the glass transition temperature of thetwo components and the T_(g) value changes according to the relativeamounts of the components. Alternatively, an incompatible blend behavesas at least two different materials and at least two tan delta peaksappear in the DMA scan. Each of the blends in the above-describedsamples exhibits a single tan delta peak between the glass transitiontemperatures of the component polymers.

Example 2

Mechanical properties, such as the tensile strength and the percentelongation at ultimate tensile strength, of the samples are tested. Theprocedure follows ASTM D882-02. A cross head speed of 20 inches perminute with a 5 kN load cell is used. The samples are conditioned at 23°C. and 50 relative humidity (RH) for twelve hours prior to testing.TABLE 1 Mechanical Properties for Films including Polymer Blends TensileStrength (MPa) Polyolefin in Blend 10 wt % 20 wt % 30 wt % EthyleneOctene (Engage 8540) 21.9 20.3 16.1 LLDPE (Equistar) 26.6 24.3 24.3 HDPE(Dow DMDA) 16.0 19.6 19.6 PP (Dow 7C50) 16.7 17.4 23.7 PP (BasellProFax) 18.1 20.7 24.0

A comparative sample including 100% Nordel 4725 EPDM as a core layer hasa tensile strength of 12.5 MPa. As illustrated in Table 1, each of thesamples exhibits a tensile strength of at least about 12 MPa. Many ofthe samples including blends in intermediate or core layers exhibit atensile strength of at least about 15 MPa and particular samples exhibita tensile strength greater than 20 MPa. In general, addition of apolyolefin to the blend of the core layer increases the tensile strengthof the sample relative to a sample including 100% Nordel 4725 EPDM inthe core layer. Particular samples, such as the sample including a blendincluding linear low density polyethylene blend and the sample includinga blend including ethylene octene copolymer exhibit peak tensilestrength at approximately 10%. Other samples exhibit an increasingtensile strength at amounts as high as 30%, such as the sample includinga blend including high density polyethylene and the sample including theblend including polypropylene block copolymer.

Percent elongation at ultimate tensile strength is also measured. Acomparative sample including 100% Nordel 4725 EPDM as a core layer hasan elongation at ultimate tensile strength of 149%. Table 2 includes thepercent elongation for the above-described samples. Each of the samplesexhibits an elongation at ultimate tensile strength of at least about147%. The sample including the ethylene octene copolymer blend exhibitsa peak percent elongation at a composition of between 10 and 20% of theethylene octene copolymer. Other samples, such as the sample includingthe LLDP blend and the sample including the polypropylene randomcopolymer blend, exhibit increasing percent elongation at 30%. TABLE 2Mechanical Properties for Films including Polymer Blends Elongation atUltimate Tensile Strength (%) Polyolefin in Blend 10 wt % 20 wt % 30 wt% Ethylene Octene 250 240 111 (Engage 8540) LLDPE (Equistar) 172 220 240HDPE (Dow DMDA) 196 205 194 PP (Dow 7C50) 198 226 223 PP (Basell ProFax)154 188 236

Example 3

Thermal behavior of a set of samples including a blend of Engage® 8540polyolefin and Nordel 4725 as a core layer are tested for thermalbehavior using a Vicat probe. Multi-layer films including a core layerencapsulated by FEP layers are formed. Samples include a core layerformed of a material selected from 100% EPDM Nordel 4725, a blendincluding Nordel 4725 and 10% Engage® 8540 polyolefin, or a blendincluding Nordel 4725 and 30% Engage® 8540 polyolefin. The samples areUV treated using an H+ bulb. In addition, an untreated sample is tested.

FIG. 1 includes a graphic illustration of probe height relative totemperature. The untreated sample exhibits a quick drop in probe heightwith increased temperature. In contrast, each of the UV treated samplesincluding polyolefin exhibit a similar change in probe height relativeto temperature to the change in probe height of the 100% EPDM sample. Assuch, the core layer may crosslink in the samples including a blend ofEPDM and as much as 30% polyolefin. In addition, the outermost layers ofFEP may adhere to layers including blends of EPDM and about 30%polyolefin or less, without the use of an intermediate adhesive layer.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true scope of the present invention. Thus, to the maximum extentallowed by law, the scope of the present invention is to be determinedby the broadest permissible interpretation of the following claims andtheir equivalents, and shall not be restricted or limited by theforegoing detailed description.

1. A multilayer film comprising: a first layer comprising a blend of apolyolefin and a diene elastomer; and a second layer directly contactingand directly bonded to the first layer, the second layer comprising afluoropolymer.
 2. The multilayer film of claim 1, wherein the dieneelastomer includes ethylene propylene diene monomer (EPDM) elastomer. 3.The multilayer film of claim 2, wherein the diene monomer of theethylene propylene diene monomer (EPDM) elastomer includes an alkenylnorborene.
 4. The multilayer film of claim 1, wherein the polyolefinincludes polypropylene.
 5. The multilayer film of claim 1, wherein thepolyolefin includes polyethylene.
 6. The multilayer film of claim 5,wherein the polyethylene includes high density polyethylene.
 7. Themultilayer film of claim 1, wherein the fluoropolymer includesfluorinated ethylene propylene copolymer (FEP).
 8. The multilayer filmof claim 1, wherein the fluoropolymer includes ethylenetetrafluoroethylene copolymer (ETFE).
 9. The multilayer film of claim 1,further comprising a third layer bonded directly to and directlycontacting the first layer.
 10. The multilayer film of claim 9, whereinthe third layer includes fluoropolymer.
 11. The multilayer film of claim1, wherein the blend includes not greater than about 40% by weight ofthe polyolefin.
 12. The multilayer film of claim 11, wherein the blendincludes not greater than about 30% by weight of the polyolefin.
 13. Themultilayer film of claim 12, wherein the blend includes not greater thanabout 20% by weight of the polyolefin.
 14. A multilayer film comprising:a first layer comprising a blend of polyolefin and ethylene propylenediene monomer (EPDM) elastomer; and a second layer directly contactingand directly bonded to the first layer, the second layer comprising afluoropolymer.
 15. The multilayer film of claim 14, wherein a dienemonomer of the ethylene propylene diene monomer (EPDM) elastomerincludes an alkenyl norborene.
 16. The multilayer film of claim 14,wherein the polyolefin includes polypropylene.
 17. The multilayer filmof claim 14, wherein the polyolefin includes polyethylene.
 18. Themultilayer film of claim 17, wherein the polyethylene includes highdensity polyethylene.
 19. The multilayer film of claim 14, wherein thefluoropolymer includes fluorinated ethylene propylene copolymer (FEP).20. The multilayer film of claim 14, further comprising a third layerbonded directly to and directly contacting the first layer.
 21. Themultilayer film of claim 20, wherein the third layer includes thefluoropolymer.
 22. The multilayer film of claim 14, wherein the blendincludes not greater than about 40% by weight of the polyolefin.
 23. Themultilayer film of claim 22, wherein the blend includes not greater thanabout 30% by weight of the polyolefin.
 24. A multilayer film comprising:a first layer comprising a blend of polyolefin and ethylene propylenediene monomer (EPDM) elastomer, the polyolefin selected from the groupconsisting of polyethylene and polypropylene; and a second layerdirectly contacting and directly bonded to the first layer, the secondlayer comprising fluorinated ethylene propylene copolymer.
 25. Themultilayer film of claim 24, wherein the polyethylene includes highdensity polyethylene.